The present invention relates generally to power converter systems, in particularly to DC-DC power converters, DC-DC power converters having input rectifiers to adapt them for AC-DC power conversion, and AC-DC power converters having control algorithms to improve power factor.
It is well known that an input power source is often not suitable for direct application to the load, and that power conversion is necessary. It is well established in the art to provide power conversion from one voltage and current level to another voltage and current level, and a high degree of sophistication has been achieved in the control and protection circuits of such converters.
It is less well recognized that the rate at which power is delivered to the load and the rate at which power is received from the input power source are often incompatible. The problem is usually recognized in the context of "noise rejection" and "frequency response to transients". It is generally addressed through the use of L-C filters and feed back control loops. The L-C filters, being resonant, are a source of some problems.
A sub-set of power converters, known generally as "high power factor AC-DC converters" does control the rate at which power is received from the input power source to provide high power factor. However, these converters are characteristically plagued with problems of energy management. Usually the voltage of a storage capacitor is sensed and used as feed-back to correct the input current control function. If its gain is too high, the power factor is compromised. The input current control function can be held constant using a latching function for each half cycle of the input AC voltage. While providing excellent power factor correction, the latching function creates a sampling limitation in the cross over frequency of the feed back control loop. Input voltage feed forward can be used to improve the response to transients in the input voltage. None the less, energy control tends to be poor, the storage capacitor is generally unnecessarily large and the control is generally subject to poor response and large overshoots.
The high power factor AC-DC converters typically have an input regulator, a storage capacitor and an output regulator essentially in series so that all of the output power must pass through both regulators.
High power factor AC-DC converters often use a boost converter for the input stage, which presents severe problems upon the application of input power and in overload conditions, or whenever the output voltage is lower than the input voltage.
It is an object of this invention to provide a DC-DC power converter in which the control of power flow and energy is improved.
It is a further object of this invention to provide an improved method of control of a DC-DC converter using feed forward techniques on the system input parameters, principally V.sub.o, I.sub.o, V.sub.i and .eta. (output voltage, output current, input voltage and efficiency).
It is a further object of this invention to provide an improved method of control of a DC-DC converter using feed forward techniques to control the converter dynamic response, using energy deficit feed forward and/or scheduling of the storage capacitor voltage as a function of the energy content of the transient response.
It is a further object of this invention to provide a DC-DC converter having controlled dynamic input resistance.
It is a further object of this invention to provide a DC-DC converter having parallel modulators for reduced losses.
It is a further object of this invention to provide a DC-DC converter using a two-input buck converter.
It is a further object of this invention to extend the application of the improved DC-DC power converter to applications requiring an AC input and to applications requiring high power factor.
It is a further object of this invention to provide a high power factor AC-DC converter using parallel modulators including a two-input buck converter, to overcome the problems associated with a boost converter input stage.